Zoos are designed to give visitors a glimpse at some of the planet’s most majestic a fearsome creatures, viewed from a safe distance and from behind protective barriers. But in this incident, caught on film at a facility in the Netherlands, that sense of security (among other things) was quite unexpectedly shattered.

In a YouTube clip provided by Dutch news source Diergaarde Blijdorp, a polar bear at the Rotterdam Zoo can be observed carrying a large stone from the bottom of its enclosure and heaving it against the glass walls of the tank. For the two men seen talking in the video, their close proximately to that iconic arctic predator doesn’t seem to sink in until the animal’s rock-tossing efforts finally make a breakthrough, causing the glass to fracture.

Officials say that the polar bear had only broken the first of five layers of glass, yet that was clear enough to humble these two on-camera zoo guests, who before seemed rather uninterested in the powerful animal in their midst.

It is, of course, impossible to say for certain if the polar bear was merely playing with rocks, or had cast the stone with liberating intent from within that glass house — but it certainly wouldn’t be the first time a captive animal tried to break out of captivity.

This scene, like so many others, inevitably raises the question as to whether it is ethical to keep otherwise wild animals confined — particularly when they just might be doing their very best to escape.